Electrical transformers are necessary components in many widely-used energy conversion systems. These systems generally relate to the generation, transmission, and utilization of electricity and operate across a broad spectrum of voltage loads. Due to the increasing costs of power generation and its transmission, engineers and scientists are continuously striving to increase the efficiency of these conversion systems. One significant improvement in efficiency has been the use of transformer cores fabricated of extremely thin laminations of an amorphous ferromagnetic strip. Amorphous magnetic strip material provides improved magnetic and electrical characteristics resulting from inherently lower electrical losses. These improved characteristics are the result in part of the thinness and higher electrical resistivity of the material. Accordingly, amorphous metal transformer cores offer improved magnetic coupling characteristics over comparable transformer cores fabricated, for example, of silicon steel laminates. Such improved magnetic coupling results in improved transformer operating efficiency offering a corresponding improvement in the operating efficiency of the energy conversion system in which it is incorporated.
Amorphous ferromagnetic metal, useful in the afore-mentioned electrical transformer application, is typically manufactured in continuous strips or ribbons of about 0.001 inch thickness. Such strips or ribbons have relatively high tensile strengths, but also have relatively poor ductility, especially after being subjected to a controlled heating cycle of a stress-relieving annealing process. Consequently, the furnace annealed amorphous ferromagnetic material is easily fractured. Accordingly, great care must be taken in the handling of the core of an electrical transformer fabricated of an amorphous metal in order to minimize undesired fracturing of the amorphous metal laminations of the core. During the operations of core fabrication, annealing, lacing of the core through a coil to form a core and coil assembly, and final transformer assembly, and in particular, during the post-anneal operations of core joint opening, lacing, and joint reclosing the amorphous ferromagnetic material is especially susceptible to fracturing and chipping.
Even during a properly aligned rejoining of the displaced core ends following coil lacing, however, some fracturing of the core material will inevitably occur. For example, handling of the core and coil assembly during and subsequent to core lacing and joint reclosure results in a necessary and unavoidable flexing of the core legs, thereby generating an unpredictable amount of chipping and separation of some fractured material from the core. Undesirably, some of this fractured amorphous material may deposit on and possibly short out the windings of the transformer coil or coils. One approach to solving this problem is to capture or contain the fractured material by a yoke-enclosing chip containment apparatus, such as that described in U.S. Pat. No. 4,673,907.
Various arrangements for restricting the flexing of the laminations of the amorphous material in order to minimize the fracture mechanism just described have been devised. However, these arrangements, such as that described in U.S. Pat. No. 4,734,975, generally teach a relatively rigid bonding agent that is applied to the noninterleaved transverse edges of the laminations so as to substantially prevent relative motion between laminations. It is also known that application of an adhesive sealant to the laminated edges of the amorphous metal laminations after winding into a core configuration forms a bonding which is essentially permanently adhered to the core and which results in a permanently sealed core structure.
Yet another problem in the fabrication of prior art wound amorphous metal cores is the necessity of maintaining the relative positions of the annealed amorphous metallic strips after lacing as closely as possible to their positions when the core was annealed. Incorrect replacement of the displaced core ends during the lacing procedure can result in large air gaps between the strips and/or significant mechanical stresses within the amorphous metal thereby impairing magnetic performance of the core, and compromising the low core loss characteristics of the amorphous material.